The invention relates to a heald shaft having a releasable end binder.
As a rule, heald shafts comprise two shaft rods which are held parallel to, and spaced from, one another by end binders. The shaft rods and the end binders together define a rectangle. To the shaft rods shaft staves are secured which support the healds. The healds have to be occasionally replaced. For such an operation at least one of the two end binders is removed, whereby the healds may be slid off the shaft staves by shifting them therealong. For effecting removal of the end binders, they are releasably coupled with the shaft rods.
German Patent Document DE 37 39 870 A1 illustrates a coupling device for connecting an end binder with a shaft rod in a web shaft. The coupling device comprises a prolongation which extends laterally away from the end binder and which extends into a cavity of the shaft rod formed as a hollow section. The prolongation is, for example, a component which has two legs which may be spread apart by an externally accessible clamping screw. The latter presses the legs against an upper and a lower web of the cavity for firmly clamping the coupling device in the cavity. In the alternative, for spreading the legs apart, a dual cam may be provided which is in engagement with respective curved follower surfaces arranged on facing sides of the legs. Upon turning the cam disposed between the legs, it spreads the legs apart for clamping the coupling device in the cavity.
Swiss Patent No. 446 221 discloses a coupling device which serves for connecting an end binder with a shaft rod and which is likewise based on cam operation. The coupling device comprises a spring element which is accommodated in the cavity and which has at least one wedge face extending at an inclination to the length direction of the shaft rod. A wedge, also disposed in the cavity, is clamped with one inclined face against the wedge face of the spring element, and is clamped with its back, for example, against a web of the shaft rod. The wedge element wedges upon imparting thereto a pulling force directed outward of the cavity. The wedge element passes through an aperture of the end binder with a prolongation acted upon by a cam provided with a lever, for generating the desired tensile force by a pivotal motion.
The two above-outlined devices are tolerance-sensitive. In case of an excess, the cam causes an excessive clamping of the coupling device. Such an occurrence is incompatible with the tendency to build shaft rods of light-weight structure. Deformations may occur if coupling devices are excessively clamped, particularly in case of light-weight shaft rods.
Further, European Published Application No. EP 0 314 181 A1 and U.S. Pat. No. 4,022,252 disclose coupling devices for interconnecting a shaft rod and an end binder, where the axially displaceable wedge of the coupling device is tightened by a tension screw. In case of sensitive heald shafts, it is necessary to tighten the screw with a torque wrench for preventing the coupling device from being excessively tightened. This requirement is occasionally neglected in practice which may result in damages.
It is therefore the object of the invention to provide an improved heald shaft.